Cam grinding machine

ABSTRACT

A cam grinding machine for grinding cams in accordance with the profile of a master cam includes two cam rollers of different diameters which may alternatively contact the master cam in accordance with the degree of wear of the grinding wheel operatively associated with the workpiece to be ground so as to reduce the lift error generated as a result of the grinding process. In order to limit the error within a tolerable range, a particularly sized roller may be utilized in conjunction with the grinding wheel until the size of the wheel has been reduced to a predetermined size due to wear at which time a smaller roller may be substituted for the original roller whereupon continued use of the original grinding wheel is permitted. In order to accurately and automatically shift the rollers into the contact position relative to the master cam, a double star gear, comprising two gears having a phase difference therebetween, is provided, rotation of the gear causing the axial movement of the rollers so as to appropriately contact the master cam.

[lite States Patent 1 Shiga et al.

1 Oct. 29, 1974 CAM GRINDING MACHINE [75] Inventors: Tokio Shiga, Okazaki; Kikuziro Nomura, Nagoya, both of Japan [73] Assignee: Toyoda Koki Kabushiki Kaisha [22] Filed: May 15, 1973 [21] Appl. No.: 360,574

[30] Foreign Application Priority Data May 15, 1972 Japan 47-48380 [52] US. Cl 51/101 R [51] Int. Cl B241) 17/00, B2413 5/16 [58] Field of Search 51/101 R, 165.77, 165.80

3,683,558 8/1972 Oishi 51/101 R Primary Examiner-Othell M. Simpson Attorney, Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier [5 7] ABSTRACT A cam grinding machine for grinding cams in accordance with the profile of a master cam includes two cam rollers of different diameters which may alternatively contact the master cam in accordance with the degree of wear of the grinding wheel operatively associated with the workpiece to be ground so as to reduce the lift error generated as a result of the grinding process. In order to limit the error within a tolerable range, a particularly sized roller may be utilized in conjunction with the grinding wheel until the size of the wheel has been reduced to a predetermined size due to wear at which time a smaller roller may be substituted for the original roller whereupon continued use ofthe original grinding wheel is permitted. In order to accurately and automatically shift the rollers into the contact position relative to the master cam, a double star gear, comprising two gears having aphase difference therebetween, is provided, rotation of the gear causing the axial movement of the rollers so as to appropriately contact the master cam.

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. 1 CAM GRINDING MACHINE BACKGROUND OF THE INVENTION 1. Field of the Invention:

2. Description of thePrior Art:

2. Description of the Prior Art:

In general, in a system for grinding a cam upon a workpiece by reproducing or duplicating a master cam, a lift error is caused upon the workpiece corresponding to the changes in the grinding point of the cam product and the wheel surface corresponding to alterations in the curvature of the grinding wheel due to a reduction in its diameter due to wear of the grinding wheel. Accordingly, the usable range of the grinding wheel diameter has been limited in conventional cam grinding machines, and in such cases, the maximum lift error of the cam has been relatively high.

In order to compensate for the lift error due to grinding wheel wear, it has previously been proposed to progressively change the master cams which have a profile designed to compensate for the wear of the grinding wheel to a predetermined degree. However, in such cases. it has been necessary to prepare several types of master cams having diverse profiles depending upon the reduction of the grinding wheel diameter due to wear. Moreover, there have been various additional disadvantages, such as for example, space limitations for housing many master cams, and low operative efficiency due to the requisite exchange of the master cams. I

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a cam grinding machine which substantially eliminates the lift error due to grinding wheel wear.

Another object of the present invention is to provide a cam grinding machine having an improved cam roller exchanging means whereby grinding wheel wear may be compensated for and an accurate reproduction of the master cam may be attained.

The foregoing objectives are achieved according to this invention through the provision of a cam grinding machine having two cam rollers of different diameters which are relatively eccentrically supported upon a roller support means so as to be tangent to a common contact plane relative to the master cam, the two cam rollers being located so as to be able to shift a distance equal to one half pitch or one and one half pitch of the master cam and being connected to a dog through indexing means associated with a traverse table, and the supporting means including a double star gear for altering the relative pitch of the master cam, whereby the two cam rollers having different diameters are respectively placed at a position so as to contact the master cam at a suitable time determined by the shifting operation of the double star gear, such gear comprising first and second integral star gears coaxially formed so as to have a one half pitch phase difference so as to compensate for the lift error caused by the grinding wheel wear.

BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features, and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the several views, and wherein:

FIG. I is a partial schematic view of the cam grinding machine constructed according to the present invention showing the principle of compensation for lift error due to grinding wheel wear;

FIG. 2 is a graph showing the relation between the optimum cam roller diameter and the grinding wheel diameter;

FIG. 3 is a sectional view of one embodiment of a cam grinding machine constructed according to present invention and showing its cooperative parts;

FIG. 4 is a sectional view taken along the line IVIV of FIG. 3;

FIG. 5 is a horizontal, partial sectional view of the apparatus of FIG. 3;

FIG. 6 is an enlarged sectional view taken along the line VI-VI of FIG. 4; and

FIG. 7 is an enlarged sectional view taken along the line VIIVII of FIG. 4.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 1 thereof, the principle of the present invention resides in the compensation for and elimination of the lift error of a cam product by altering the cam roller diameter corresponding to a decrease in the grinding wheel diameter. As seen in FIG. 1, a workpiece W can be processed without visible error by coaxially rotating a master cam MC together with the workpiece W by contacting the master cam with a cam roller, the cam roller radius being Ro which corresponds to the maximum grinding wheel radius Rk of a wheel which has not been worn. v

When the grinding wheel radius is reduced to Rt due to wear, the cam roller radius should be Rp, and the rotational center is shifted from P0 to P so that the roller surface is always tangent to a plane as at Q, while the center of the grinding wheel is advanced by a distance Rk-Rt which is equal to the degree of wear upon the grinding wheel. Accordingly, even though the grinding wheel radius is decreased, the lift error of the cam product can be reduced by appropriately changing the cam roller radius.

Turning now to FIG. 2, when the lift error is zero as shown by the solid line, the cam roller radius should be continuously changed. When an allowable tolerance fl/Z is considered, as shown by the chain lines, the cam roller radius can be changed in a step-wise manner depending upon the decrease in the grinding wheel radius. An allowable tolerance of 1-5 is shown by the double dotted chain line. When the lift error of the cam product is maintained within the allowable tolerance 25. an error of about 8 initially results from reproducing the cam when grinding under the conditions wherein the grinding wheel diameter is d and the cam roller diameter is B, and subsequently, the error is gradually reduced, depending upon the wear of the grinding wheel, to zero and still later the error is gradually increased to approximately +6 when the grinding wheel diameter becomes b, which is the limitation for using the cam roller having a diameter B.

Accordingly, when a cam is grounded by exchanging the cam roller with a new cam roller having a diameter A, an error of about 8 is given, and the grinding wheel can be used for a longer period of time, that is until the grinding wheel diameter is a which causes an error of +6 and which is the limitation for using the cam roller having the diameter A. In order to use the grinding wheel, within the diametrical range of a to a, a cam roller having a diameter A and a cam roller having a diameter B are utilized, and when the grinding wheel diameter is decreased to b, the cam roller is exchanged, and it is consequently possible to reproduce the cam product with an error of less than the allowable tolerance of :8. The maximum lift error can be limited within the range of by exchanging the cam roller with another cam roller having different radii at suitable times during the operation.

Referring now to FIGS. 3 and 4, one embodiment of a grinding machine constructed according to the present invention and by means of which the aforementioned principles may be practiced is illustrated as including a traverse table 2 which is slidably mounted upon a bed 1 and a pivotable table 4 which is rotatably mounted through means of a supporting shaft 5 upon bearings 3 disposed upon the upper planar surface of traverse table 2. A spindle 7 disposed within a tubular master cam 6, is journaled within bearings 8 and 9 which are mounted upon table 4, and a foot-stock 10, having its workpiece axis aligned with the spindle axis, is also mounted upon table 4. Accordingly, a workpiece W, such as for example, a cam shaft, may be interposed between the table head and the foot-stock 10, rotated by means of a driving dog associated with the spindle 7, and ground by means of a grinding wheel 11 disposed laterally of the workpiece.

At the rear part of the spindle 7, there is provided a brake drum l2 and a universal joint 13 about which spindle 7 may pivot or rotate as a result of a rotational force transmitted through means of a worm 16 and a worm wheel 17 which is mechanically connected with an intermediate shaft 18, and a transmission shaft 19 which is connected to another universal joint 20 and a spline shaft 21, the drive means being an electric motor mounted upon the reduction box 14 which is disposed upon the upper planar surface of traverse table 2 and which houses the noted transmission. A supporting bracket 22 is fixed to one side of the table 4 and a spring 25 is secured between the bracket 22 and an adjustable rod 24 which is secured upon the head-stock so as to be adjustable in the vertical direction. A rotational moment is thus impressed upon table 4 by means of the spring force whereby contact pressure is provided between the below-mentioned cam roller and the master cam 6. The spindle 7 and table 4 extend within a head-stock housing 23 and one end of a piston rod, disposed within a cylinder 26 which is mounted within housing 23, is located adjacent to and may act upon bracket 22 so as to return the table 4 to a given position against the force of the spring 25 thereby limiting the rotational movement of table 4.

A cam roller supporting means 28 is mounted in a cantilever fashion upon a dovetailed track 27 which is secured to the head-stock housing 23 so as to be movable in a direction parallel to the spindle axis, and as shown in FIG. 5, a cam roller supporting shaft 29 is secured within the roller supporting means 28, two cam rollers 30 and 31, having different radii corresponding to the master cam 6, being rotatably secured upon one end of the roller supporting shaft 29. The larger roller 30 is utilized when the range of the grinding wheel diameter is d to b so as to compensate for the lift error within an allowable tolerance range, and the smaller roller 31 is utilized when the range of the grinding wheel diameter is b to a so as to also compensate for the lift error within an allowable tolerance range.

The large roller 30 is coaxially mounted upon the roller supporting shaft 29 while the smaller roller 31 is eccentrically supported upon the same shaft, the center P of roller 31 being offset from the center P0 of the roller 30 by an amount equal to the radial difference, i.e., Ro-Rp. Accordingly, one point of the peripheral surfaces of both rollers is always tangent to a common plane, as shown at Q in FIG. 1. When the master cam 6 is pivoted along with table 4 about shaft 5 so as to contact the cam rollers 30 and 31, the spindle 7 as well as the workpiece W are subsequently rotated according to the master cam profile in order that the desired cam profile movement of the workpiece W can be attained. With regard to the pitch interval between the large roller 30 and the smaller roller 31, in order to prevent any interference of one of the rollers with respect to an adjacent master cam when the other roller is being correspondingly operated with respect to another master cam, the rollers are arranged so as to have a pitch differential of 1.5 p in the axial direction when the pitch differential between cams 6 is 1p. Accordingly, the roller supporting means 28 is indexed and shifted to the position wherein either the larger cam roller 30 or the smaller cam roller 31 contacts the master cam 6, the shift operation being performed by meanS of the below-mentioned double star gear, generally indicated by the reference character 36. Naturally, the interval between the larger roller 30 and the smaller roller 31 can alternatively be 0.5p in order to similarly prevent interference.

Referring again to FIG. 4, the indexing mechanism of the roller supporting means 28 is illustrated as including a rack 32 which is fixed to the lower surface of the roller supporting means 28 and a gear 33 which is rotatably mounted upon the head-stock 23 and which intermeshes with the rack 32. The double star gear 36 is provided with a key so as to be slidable, in a relative axial direction, within an appropriate slot of a rotary shaft 35 which supports a gear 34 which intermeshes with the gear 33. In a normal indexing operation, the roller supporting means 28 is relatively shifted a distance equal to the pitch of the master cam 6 by rotation of the double star gear 36, the rotation of the double star gear 36 also causing a one tooth relative shift of a dog 38 fixed upon a dog bar 37 which is secured upon the dog supporting table 1a which forms a part of bed 1. The traverse table 2 is thus indexed a predetermined interval whereby the relative position between the cam workpiece product and the grinding wheel can be altered, and the relative position between the cam rollers 30 and 31 and the master cam 6 is automatically altered.

The first and the second star gears 39 and 40 are integrally formed in one piece, the gears being coaxially spaced and the composite gear 38 is H-shaped in crosssection. As shown in FIG. 6, each of the gears has 6 teeth formed upon the peripheral portion thereof and the gears are arranged so that a 1/2 pitch phase difference exists therebetween. Accordingly, the phase difference between the first and the second star gears is 30, while the distance equal to the pitch of the first and the second star gears 39 and 40 is 60, and the roller supporting means 28 may be indexed and shifted the distance equal to the pitch relative to the star gears 39 and 40 by means of rotating the star gears 39 and 40 by an amount equal to 60.

In order to accomplish the aforementioned shifting and indexing operations, a cylinder 42 is fixed upon a holding table 41 which is secured to the rear portion of the head-stock 23, a piston 43, having an integral piston rod 44 associated therewith, being slidably received within the cylinder, the piston and rod extending parallel to the rotary shaft 35, as best seen in FIG. 7. A shifter fork 45 has one end fixedly mounted within the annular groove provided between the first and second star gears and has its other end secured to the free end of the piston rod 44. In this manner, either of the first or second star gears may be shifted to a position so as to engage the dog 38.

As shown in FIGS. 4, 5 and 7, the first star gear 39 is engaged with the dog 38 and the larger roller 30 is in contact with the master cam 6. When the relationship is altered whereby the smaller roller 31 is in contact with the master cam 6, the double star gear 36 is shifted by means of the operation of the cylinder piston 43 whereby the dog 38 is brought into engagement with the second star gear 40 at the time of the first indexing operation of the traverse table 2. Accordingly, the double star gear 36 which has a phase difference of 90 due to the rotation equal to the gear pitch plus the phase difference of 30 between the gears 39 and 40, is rotated, and the roller supporting means 28 is shifted an interval equal to the pitch of the master cam 6. Only upon the first index shifting of the double star gear 36 is the roller supporting means shifted for the interval difference between the larger roller 30 and the smaller roller 31, that is 1.5 pitch, so that the position at which the smaller roller 31 contacts the master cam 6 is attained by the indexing operation.

Referring now to FIGS. 4, 5 and 6, another cylinder 46 is also fixed to the holding table 41, and a piston 47, having an integral piston rod 48, is slidably received within the cylinder, the rod 48 extending parallel to the spindle axis. At the free end of the piston rod 48, there is provided a pivoting means 49 which has associated therewith a pivotable ratchet 50 which may be interconnected with one of the star gears engaging the dog 38. The ratchet 50 serves to rotate the double star gear 36 in a direction opposite to the initial rotation when engaged with the dog 38, whereby the double star gear 36 is rotated in the opposite direction for an interval equal to the gear pitch or 60 by means of one operative stroke of the cylinder 46. Consequently, when the piston 47 slides to the left as seen in FIG. 6, the ratchet 50 is forced upon the stopper surface 49a of the pivoting means 49 by means of a spring 52, whereupon the double star gear 36 is rotated. When the piston 47 slides to the right as seen in FIG. 6, the ratchet 50 is maintained in the position tending to press the same upon the inclined surface 4% of the pivoting means 49,

sponds to the profile of the master cam 6, and accordingly, the grinding wheel 11 is only advanced an amount corresponding to the predetermined size of the workpiece W. During the initial stage of the operation, the larger roller 30 is in contact with the master cam 6 and the first star gear 39 is positioned so as to contact the dog 38 whereupon a grinding process may be performed in a manner similar to that of a conventional machine. In such manner, when the machine is shifted from one cam to an adjacent cam, the indexing of the traverse table 2 is performed at the same time as when the indexing of the roller supporting means 28 is performed through means of the dog 38 fixed to the dog bar 37, the first star gear 39, and the gears 33 and 34 and rack 32, whereby the adjacent master cam 6 is now in contact with the larger roller 30 through means of shifting the roller supporting means 28 an interval equal to the cam pitch, and the next cam workpiece product may be ground corresponding to the new master cam 6. In this manner, the cams are progressively ground and the radius of the grinding wheel 11 is decreased with suitable dressing.

The grinding wheel radius may be indicated by means of a counter or meter, or as an alternative, the grinding wheel wear may be detected in a manner similar to detection of the position of the dressing tool, such as for example, a limit switch, so that the apparatus may be shifted from the larger roller 30 to the smaller roller 31, when the grinding wheel radius is b as shown in FIG. 2. When the grinding operation for the cam reproduction is finished through contact between the larger roller 30 and the master cam 6, and the traverse table 2 is returned to the original position, the double star gear 36 is shifted to the position connecting the second star gear 40 with the dog 38 by supplying hydraulic oil to the cylinder 42. When the traverse table 2 is indexed as a result of such shift, the second star gear 40, having a phase difference of which is due to the gear pitch plus the phase difference existing between the first and the second star gears, is rotated so that the roller supporting means 28 is shifted by a distance equal to 1.5 pitch compared to the conventional one pitch shift, whereby the smaller roller 31 is now in contact with the master cam 6. Hence, the position is the original position of the traverse table 2 utilizing the smaller roller 31.

The roller supporting means 28 is shifted a distance equal to the cam pitch, due to the indexing of the traverse table 2 in the subsequent operations, whereby the cam reproduction is performed by means of grinding in the same manner. The relative condition preventing the lift error by decreasing the grinding wheel radius can thus be given by the operation whereby the lift error of the cam workpiece product is decreased and the range throughout which the grinding wheel is usable is remarkably increased. The cam reproduction is further continued by utilizing the smaller roller 31, whereby the radius of the grinding wheel 11 is further decreased by suitable dressing. When the grinding wheel diameter is decreased to a as shown in H0. 2, the grinding wheel 11 is replaced with a new grinding wheel having a maximum diameter d as is also shown in FIG. 2. Accordingly, the apparatus is again switched from the smaller roller 31 to the larger roller 30.

In such instance, at the right forward position of the traverse table 2 at the time of finishing the cam reproduction by utilizing the smaller roller 31, hydraulic oil is supplied to the cylinder 42 whereby the double star gear 36 is shifted to the position at which the first star gear 39 is connected with the dog 38, and subsequently, the traverse table 2 is returned to the original position, so that the roller supporting means 28 is shifted a distance equal to 1.5 pitch at the time of indexing the first return of the traverse table 2. Accordingly, the larger roller 30 is in contact with the master cam 6.

When the apparatus is switched from the smaller roller 31 to the larger roller 30, the traverse table 2 is returned to the original position in the condition wherein the smaller roller 31 is in contact with the master cam 6, and consequently, the double star gear 36 is shifted by the cylinder 42, and the traverse table 2 is indexed the equivalent distance of the cam pitch, whereby the larger roller 30 faces the master cam 6. it is noted however, that at such time of positioning the larger roller 30, such roller contacts the master cam 6 at a position which is advanced a distance equal to three times the pitch from the corresponding position of the first master cam 6. Accordingly, the first star gear 39 msut be rotated in the opposite direction the equivalent dis tance or 180 by means of the corresponding operation of the cylinder 46 so that the roller supporting means 28 and the larger roller 30 may be returned to the original position at which the same contacts the first master cam 6 As stated above, in accordance with this invention, the lift error of the cam product can be remarkably reduced by changing the cam roller radius depending upon the corresponding decrease in the grinding wheel radius so as to obtain a product having a high degree of accuracy and to increase the usable range of the grinding wheel radius in comparison with the operative ranges of conventional grinding wheels. in accordance with this invention, the larger roller and the smaller roller are arranged to shift a relative distance equal to one half the pitch of the master cams, and the double star gear consisting of the first and second star gears having a one-half pitch phase difference, is used as a star gear for moving the cam roller at the same time that the traverse table is indexed so that when the cam rollers are changed to compensate for the decrease in the grinding wheel radius, the traverse table can be indexed only by shifting the double star gear, whereby the automatic indexing mechanism for the roller supporting means can be simplified. Moreover, when the apparatus is shifted from the smaller roller to the larger roller, the operation is facilitated to quite an extent due to the provision of a reversing device for returning the double star gear in the opposite direction at a predetermined rate.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. lt is to be understood therefore that within the scope of the appended claims the present invention may be practiced otherwise than as specifically described herein.

We claim:

1. In a cam grinding machine having a master cam of a predetermined profile which is pivotably supported, and axially aligned and synchronously rotated with a workpiece, and which contacts under pressure, a cam roller which is relatively indexed upon a movable traverse table for suitably accomplishing the cam reproduction by grinding, whereby the workpiece is ground by a grinding wheel, the improvement comprising:

a bed slidably supporting said movable traverse table;

a roller supporting means mounted upon said traverse table which is movable in a direction parallel to the axis of said master cam;

said master cam including a plurality of coaxially disposed cam members, the axial distance between said cam members comprising the pitch interval of said master cam;

a large roller and a small roller respectively supported by said roller supporting means so as to have a point of contact with said master cam within a common plane and which are arranged to shift a distance of one half pitch relative to the pitch interval of said master cam;

a rotary shaft rotatably supported by said traverse table and adapted to be rotated at the same time as said traverse table is movably indexed so as to shift said roller supporting means said predetermined amount;

a double star gear shiftably and rotatably connected with said rotary shaft having first and second star gears, said gears having a half phase difference therebetween;

a dog fixed upon said bed for engaging said double star gear when said traverse table is indexed; and

shifting means for shifting said double star gear to a position wherein said dog fixed upon said bed supporting said table is connected to either said first or second star gear,

whereby said double star gear may be shifted depending upon the decrease in the grinding wheel radius so as to compensate for the lift error caused by said decrease in said grinding wheel radius within an allowable tolerance and simultaneously said roller supporting means may be shifted by indexing said traverse table so as to shift said large roller contacting said master cam to said small roller for contacting said master cam.

2. A cam grinding machine as set forth in claim 1,

which further comprises:

reverse means for reversely rotating said double star gear a predetermined amount so as to contact said master cam with said large roller at the time of retracting said double star gear so as to shift the relative positions of said smaller roller and said large roller at the same time of appropriately returning and indexing said traverse table,

whereby said master cam is relatively shifted from a position wherein said cam contacts said small roller to a position wherein said cam contacts said large roller.

3. In a cam grinding machine having a master cam pivotably supported and axially aligned and synchronously rotated with a workpiece, and which contacts,

under pressure, a cam roller which is indexed by driving means with a movable traverse table upon a bed so as to properly attain cam reproduction by grinding,

whereby the workpiece is ground by a grinding wheel, the improvement comprising:

a roller supporting means slidably mounted upon said traverse table;

said master cam including a plurality of coaxially disposed cam members, the axial distance between said cam member comprising the pitch interval of said master cam;

two cam rollers rotatably supported and arranged upon said roller supporting means so as to have a one half pitch interval difference relative to the pitch interval of said master cam;

a rotary shaft rotatably mounted upon said traverse table;

means for drivingly connecting said rotary shaft and said roller supporting means;

a double star gear shiftably mounted upon said rotary shaft, said double star gear comprising first and second star gears which have a one half pitch phase difference therebetween said corresponds to the pitch difference of said cam rollers relative to said master cam;

dogs fixed upon said bed for engaging said double star gear when said traverse table is indexed; and

shifting means for shifting s'aid double star gear so as to cause either of said first or second star gears to engage said dogs.

4. A cam grinding machine as set forth in claim 3, wherein said double star gear and said rollers are shifted when the decrease in the grinding wheel radius is below a predetermined value so as to compensate for the lift error caused by said decrease in the grinding wheel radius within an allowable tolerance.

5. A cam grinding machine as set forth in claim 3, wherein said roller supporting means is shifted by indexing said traverse through said driving connecting means so as to shift from one of said cam rollers contacting said master cam to the other of said cam rollers.

6. A cam grinding machine as set forth in claim 3, which further comprises:

reverse means for reversely rotating said double star gear a predetermined amount so as to contact said master cam with said large roller at the time of retracting said double star gear so as to shift the relative positions of said small cam roller and said large cam roller at the same time of appropriately returning and indexing said traverse table,

whereby said master cam is relatively shifted from a position wherein said cam contacts said smaller roller to a position wherein said cam contacts said large roller.

7. In a cam grinding machine having a master cam pivotably supported and axially aligned and synchronously rotated with a workpiece, so as to be in contact with, under pressure, a cam roller which is indexed by driving means with a movable traverse table upon a bed so as to properly index and attain cam reproduction by grinding, whereby the workpiece is ground by a grinding wheel, the improvement comprising:

a roller supporting means slidably mounted upon said traverse table;

said master cam including a plurality of coaxially disposed cam members, the axial distance between said cam members comprising the pitch interval of said master cam;

large and small cam rollers which are rotatably supported and arranged upon said roller supporting means so as to have a one half pitch interval difference relative to the pitch interval of said master cam;

a rotary shaft rotatably mounted upon said traverse table;

means for drivingly connecting said rotary shaft and said roller supporting means;

a double star gear shiftably mounted upon said rotary shaft, said double star gear comprising first and second star gears which have a one half pitch phase difference therebetween which corresponds to the pitch difference of said cam rollers relative to said master cam;

dogs fixed upon said bed for engaging said double star gear when said traverse table is indexed; and

large roller and will contact said small cam roller. 

1. In a cam grinding machine having a master cam of a predetermined profile which is pivotably supported, and axially aligned and synchronously rotated with a workpiece, and which contacts under pressure, a cam roller which is relatively indexed upon a movable traverse table for suitably accomplishing the cam reproduction by grinding, whereby the workpiece is ground by a grinding wheel, the improvement comprising: a bed slidably supporting said movable traverse table; a roller supporting means mounted upon said traverse table which is movable in a direction parallel to the axis of said master cam; said master cam including a plurality of coaxially disposed cam members, the axial distance between said cam members comprising the pitch interval of said master cam; a large roller and a small roller respectively supported by said roller supporting means so as to have a point of contact with said master cam within a common plane and which are arranged to shift a distance of one half pitch relative to the pitch interval of said master cam; a rotary shaft rotatably supported by said traverse table and adapted to be rotated at the same time as said traverse table is movably indexed so as to shift said roller supporting means said predetermined amount; a double star gear shiftably and rotatably connected with said rotary shaft having first and second star gears, said gears having a half phase difference therebetween; a dog fixed upon said bed for engaging said double star gear when said traverse table is indexed; and shifting means for shifting said double star gear to a position wherein said dog fixed upon said bed supporting said table is connected to either said first or second star gear, whereby said double star gear may be shifted depending upon the decrease in the grinding wheel radius so as to compensate for the lift error caused by said decrease in said grinding wheel radius within an allowable tolerance and simultaneously said roller supporting means may be shifted by indexing said traverse table so as to shift said large roller contacting said master cam to said small roller for contacting said master cam.
 2. A cam grinding machine as set forth in claim 1, which furthEr comprises: reverse means for reversely rotating said double star gear a predetermined amount so as to contact said master cam with said large roller at the time of retracting said double star gear so as to shift the relative positions of said smaller roller and said large roller at the same time of appropriately returning and indexing said traverse table, whereby said master cam is relatively shifted from a position wherein said cam contacts said small roller to a position wherein said cam contacts said large roller.
 3. In a cam grinding machine having a master cam pivotably supported and axially aligned and synchronously rotated with a workpiece, and which contacts, under pressure, a cam roller which is indexed by driving means with a movable traverse table upon a bed so as to properly attain cam reproduction by grinding, whereby the workpiece is ground by a grinding wheel, the improvement comprising: a roller supporting means slidably mounted upon said traverse table; said master cam including a plurality of coaxially disposed cam members, the axial distance between said cam member comprising the pitch interval of said master cam; two cam rollers rotatably supported and arranged upon said roller supporting means so as to have a one half pitch interval difference relative to the pitch interval of said master cam; a rotary shaft rotatably mounted upon said traverse table; means for drivingly connecting said rotary shaft and said roller supporting means; a double star gear shiftably mounted upon said rotary shaft, said double star gear comprising first and second star gears which have a one half pitch phase difference therebetween said corresponds to the pitch difference of said cam rollers relative to said master cam; dogs fixed upon said bed for engaging said double star gear when said traverse table is indexed; and shifting means for shifting said double star gear so as to cause either of said first or second star gears to engage said dogs.
 4. A cam grinding machine as set forth in claim 3, wherein said double star gear and said rollers are shifted when the decrease in the grinding wheel radius is below a predetermined value so as to compensate for the lift error caused by said decrease in the grinding wheel radius within an allowable tolerance.
 5. A cam grinding machine as set forth in claim 3, wherein said roller supporting means is shifted by indexing said traverse through said driving connecting means so as to shift from one of said cam rollers contacting said master cam to the other of said cam rollers.
 6. A cam grinding machine as set forth in claim 3, which further comprises: reverse means for reversely rotating said double star gear a predetermined amount so as to contact said master cam with said large roller at the time of retracting said double star gear so as to shift the relative positions of said small cam roller and said large cam roller at the same time of appropriately returning and indexing said traverse table, whereby said master cam is relatively shifted from a position wherein said cam contacts said smaller roller to a position wherein said cam contacts said large roller.
 7. In a cam grinding machine having a master cam pivotably supported and axially aligned and synchronously rotated with a workpiece, so as to be in contact with, under pressure, a cam roller which is indexed by driving means with a movable traverse table upon a bed so as to properly index and attain cam reproduction by grinding, whereby the workpiece is ground by a grinding wheel, the improvement comprising: a roller supporting means slidably mounted upon said traverse table; said master cam including a plurality of coaxially disposed cam members, the axial distance between said cam members comprising the pitch interval of said master cam; large and small cam rollers which are rotatably supported and arranged upon said roller supporting means so as to have a one half pitch interval diffErence relative to the pitch interval of said master cam; a rotary shaft rotatably mounted upon said traverse table; means for drivingly connecting said rotary shaft and said roller supporting means; a double star gear shiftably mounted upon said rotary shaft, said double star gear comprising first and second star gears which have a one half pitch phase difference therebetween which corresponds to the pitch difference of said cam rollers relative to said master cam; dogs fixed upon said bed for engaging said double star gear when said traverse table is indexed; and shifting means for shifting said double star gear so as to cause either of said first or second star gears to engage said dogs, whereby said double star gear is shifted when the decrease in the grinding wheel radius is below a predetermined value so as to compensate for the lift error caused by said decrease in the grinding wheel radius within an allowable tolerance, and simultaneously said roller supporting means is shifted by indexing said traverse table so as to shift said rollers whereby said master cam will cease to contact said large roller and will contact said small cam roller. 